Our objectives are to define the molecular and functional properties of molecules responsible for adhesion of Langerhans cells (LC) and dendritic epidermal T cells (DETC) to keratinocytes (KC) in mouse epidermis and to study the cell-cell communication that follows ligation of these molecules. Working hypotheses are that: 1) LC and DETC express specialized adhesion molecules that bind to appropriate ligands on KC; and 2) ligation of these molecules transduces signals that regulate the immunologic functions of LC, DETC and KC. These hypotheses are based on observations that both LC and DETC reside within epidermis and home preferentially to skin following intravenous infusion; on findings that LC and DETC, but not splenic dendritic cells nor T cells, bind selectively to KC monolayers via apparently "unique" receptor-ligand interactions; and on data that indicate adhesion molecules to be capable not only of mediating cell movement and localization, but also of transducing signals that regulate immunologic functions of leukocytes. Specific aims are: 1) To characterize receptor-ligand interactions responsible for LC and DETC adhesion to KC. Methods include cell adhesion assays and blocking with specific inhibitors of known adhesion molecules. 2) To identify the molecules that mediate LC and DETC binding to KC. Principal methodology is cell precipitation in which adhesion molecules in solubilized form bind to their respective ligands and are precipitated with cells that express these ligands. 3) To purify and characterize adhesion molecules at protein levels. Strategies include purification by combination of cell precipitation and avidin-affinity chromatography, amino acid sequencing and production of polyclonal Ab and mAb against these molecules. Purified molecules will be analyzed for binding properties, tissue distribution, and antigenic cross-reactivity to known adhesion molecules. 4) To study whether ligation of adhesion molecules transduces signals that lead to modulation of the immunologic functions of LC, DETC and KC. Strategies include coupling of adhesion molecules with purified ligands or with Ab, cytokine bioassays, and mRNA analysis by the reverse transcriptase polymerase chain reaction. These studies will provide new knowledge concerning mechanisms of leukocyte homing to epidermis and of heterotypic cell-cell communication in epidermis. This knowledge will be applied in subsequent proposals to identify the human equivalents of these molecules and to study the pathogenesis of leukocyte epidermotropism and of tumor cell invasion in selected skin disorders.